Geochemistry of Metal and Metalloid Thioanions

HELZEAR-0229387本项目将探索选定的含硫阴离子的地球化学性质。硫代阴离子由至少部分与硫化物离子配位的金属或类金属阳离子组成。这些阴离子在自然界中的化学行为几乎没有得到研究。所获得的信息可应用于固体(包括核废料)的管理、提高我们对成矿作用的理解、重建海洋过去的氧化还原状态和修复海岸生态系统等领域。我们将以前人对硫化物水域中钼行为的研究为原型，探索触发稀土颗粒缔合的机制。这一元素在古环境研究、地质年代学以及作为核废料成分T_c的实验室模型中具有重要意义。在含氧环境中，稳定形式是亲水性很强的ReO4-。在缺氧到缺氧的环境中，Re变得与粒子相关。可能引发这种行为变化的机制包括转化为硫代二氢呋喃或还原为REIV复合体。形成的产物的性质和表征这种变化的平衡常数是这部分项目的目标。已观察到硫钼酸根离子能溶解非常难溶的铁矿物，如黄铁矿。表明形成了较强的Fe-Mo-S络合物。我们将对这一现象进行系统的研究，以便对溶解的络合物进行表征。如果这种络合物能够与黄铁矿发生可逆平衡，那么它们可以催化单硫化铁矿物的形成。黄铁矿的形成机制仍然是地球化学家们非常感兴趣的一个领域(也存在一些争议)，尽管之前已经做了相当多的工作。我们发现CuI与硫代亚砷酸根离子AsS(OH)(SH)-之间存在非常强的络合作用，这引起了理论界的兴趣，并导致了其他潜在危险金属(如Pb2+，Hg2+)与类似强的硫代亚砷酸根络合物的预测。我们将检验这些预测。这类络合物导致危险金属和类金属的协同共运输。它们应该在用于设计危险废物场地和就疏浚废渣、尾矿等的处置选择作出决定的计算模型中考虑在内。

HelzEAR-0229387This project will explore the geochemistry of selected aqueous thioanions. Thioanions consist of a metal or metalloid cation coordinated at least partially by sulfide ions. The chemical behavior of these anions in nature has received little study. The information obtained could have applications in such diverse areas as managing solid (including nuclear) wastes, improving our understanding of ore formation, reconstructing the past redox status of the ocean and healing coastal ecosystems.Using previous studies of Mo behavior in sulfidic waters as a prototype, we will explore mechanisms that trigger particle-association of Re. This element is of interest in paleoenvironmental studies, in geochronology and as a laboratory model of the nuclear waste component, Tc. In oxic environments, the stable form is strongly hydrophilic ReO4-. In suboxic to anoxic environments, Re becomes particle-associated. Mechanisms that could trigger this change in behavior include transformation to thioperrhenates or reduction to ReIV complexes. The nature of the products formed and equilibrium constants characterizing such changes are the objective of this portion of the project.Thiomolybdate ions have been observed to dissolve very insoluble Fe minerals, like pyrite. Formation of strong Fe-Mo-S complexes is implied. We will study this phenomenon systematically in order to characterize the dissolved complexes. If such complexes are capable of reversible equilibrium with pyrite, then they may catalyze formation of this mineral from Fe monosulfide. Mechanisms of pyrite formation remain an area of active interest (and some dispute) among geochemists, despite considerable previous work. Our discovery of very strong complexing between CuI and the oxythioarsenite ion, AsS(OH)(SH)-, has sparked interest from theorists and led to predictions of similarly strong thioarsenite complexes involving other potentially hazardous metals (e.g. Pb2+, Hg2+). We will test these predictions. Complexes of this kind result in synergistic co-transport of hazardous metals and metalloids. They should be accounted for in computational models used for designing hazardous waste sites and making decisions about disposal options for dredge spoil, mine tailings, etc.